The genetic basis of myelodysplastic syndromes (MDS) is heterogeneous, and various combinations of somatic mutations are associated with different clinical phenotypes and outcomes. Whether the genetic basis of MDS influences the outcome of allogeneic hematopoietic stem-cell transplantation (HSCT) is unclear. Patients and MethodsWe studied 401 patients with MDS or acute myeloid leukemia (AML) evolving from MDS (MDS/ AML). We used massively parallel sequencing to examine tumor samples collected before HSCT for somatic mutations in 34 recurrently mutated genes in myeloid neoplasms. We then analyzed the impact of mutations on the outcome of HSCT. ResultsOverall, 87% of patients carried one or more oncogenic mutations. Somatic mutations of ASXL1, RUNX1, and TP53 were independent predictors of relapse and overall survival after HSCT in both patients with MDS and patients with MDS/AML (P values ranging from .003 to .035). In patients with MDS/AML, gene ontology (ie, secondary-type AML carrying mutations in genes of RNA splicing machinery, TP53-mutated AML, or de novo AML) was an independent predictor of posttransplantation outcome (P = .013). The impact of ASXL1, RUNX1, and TP53 mutations on posttransplantation survival was independent of the revised International Prognostic Scoring System (IPSS-R).Combining somatic mutations and IPSS-R risk improved the ability to stratify patients by capturing more prognostic information at an individual level. Accounting for various combinations of IPSS-R risk and somatic mutations, the 5-year probability of survival after HSCT ranged from 0% to 73%. ConclusionSomatic mutation in ASXL1, RUNX1, or TP53 is independently associated with unfavorable outcomes and shorter survival after allogeneic HSCT for patients with MDS and MDS/AML. Accounting for these genetic lesions may improve the prognostication precision in clinical practice and in designing clinical trials.

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612 Recent work has shown that acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS) patients exhibit downregulation of miR-146a, a miRNA that negatively regulates the innate immune pathway by targeting IRAK1 and TRAF6. Mice lacking miR-146a show elevated IRAK1 protein expression, and develop AML and MDS-like features resembling the human diseases. Prior to this study, the role of IRAK1 in human myeloid malignancies was unknown. We conducted a comparison of gene expression profiles of 136 cases of MDS CD34+ cells with 17 normal CD34+ cells obtained from ArrayExpress (E-GEOD-19429; Pellagatti et al., Leukemia, 2010). According to this data set, we observed IRAK1 overexpression in MDS patients (P = 0.017). IRAK1 is a serine/threonine kinase, and after phosphorylation on threonine-209 (T209), its kinase activity is induced, thus allowing for subsequent activation of TRAF6 and eventually NF-kB. Interestingly, we observed higher basal levels of phospho-IRAK1 at T209 in MDS and AML samples as compared to normal human CD34+ cells. To investigate the potential role of IRAK1 in AML and MDS, we used genetic and pharmacological approaches to suppress IRAK1 activity in MDS/AML cell lines and bone marrow cells from MDS patients. RNAi-mediated knockdown of IRAK1 in MDS and AML samples resulted in impaired growth of malignant hematopoietic stem/progenitor cells in methylcellulose assays and rapid apoptosis in vitro. In addition, we used a small-molecule inhibitor (benzimidazole analog; Amgen Inc.) to potently inhibit IRAK1 kinase activity. MDS/AML cell lines and MDS patient samples cultured with the IRAK1 inhibitor exhibited impaired growth and increased apoptosis, which coincided with decreased phospho-IRAK1 at T209, and active versions of TRAF6 and NF-kB. Importantly, the inhibition of IRAK1 kinase function is selectively detrimental to MDS and AML samples while preserving normal CD34+ cell viability and function. Given this novel requirement of IRAK1 in MDS and AML, we examined whether Lenalidomide or Bortezomib, two treatment options for MDS/AML and reported immunosuppressors, exhibit anti-leukemic activity in part by targeting IRAK1. We observed that Bortezomib, but not Lenalidomide, inhibits IRAK1 mRNA and protein expression in MDS/AML cells. The cytotoxic effect of Bortezomib can be partly rescued by forced expression of IRAK1 in these cells. To determine the molecular and cellular basis of cell death following loss of IRAK1 function or expression, we applied microarrays to MDS cells treated with IRAK1 inhibitor or transduced with a lentiviral vector encoding an shRNA targeting IRAK1. An overlap of commonly deregulated genes imposed by loss of IRAK1 expression or by the IRAK1 inhibitor revealed unique pathways relevant to the survival of MDS and AML cells. In summary, these findings are the first to implicate IRAK1 in the maintenance of myeloid malignancies and describe the effectiveness of an IRAK1 inhibitor on suppressing MDS and AML viability. Disclosures: Oliva: Celgene: Consultancy.